When the posh architectural firm Skidmore, Owings, and Merrill designed the Chemsunny World Trade Center in Beijing, it was more efficient than a typical glass-walled luxury building in China. The fifteen-story building, formed of three connected towers, boasted a 50,000-square-meter “double skin breathing” glass wall—two panels of glass sandwiching a layer of air circulating between—which was about 40 percent more energy efficient than a typical glass facade. The building’s interlocking geometrical design, influenced by Chinese calligraphy, allowed for an expansive atrium and plenty of natural light. A large rooftop garden, irrigated with recycled water, provided a critical cooling effect.

The building was completed in 2006. When I toured the building last month, it wasn’t merely to admire the design. The building had already undergone an energy efficient retrofit.

The double-skin breathing glass wall is 40 percent more energy-efficient than normal glass.

China is still putting up buildings at an astonishing pace, although perhaps slightly slower now than its peak a few years ago, when it was estimated that China built 2 billion square meters of building space—the equivalent of every building in Canada—each year. The World Bank estimated in 2010 that nearly half of all the buildings constructed in the world over the next two decades would be in China.

China’s building sector accounts for more than 25 percent of China’s energy use, and Chinese buildings are on track to become responsible for one-fifth of the world’s coal consumption by 2020—stretching the limits of what China can supply. Improving the efficiency of its buildings, new and old, is a key part of China’s strategy to reduce energy demand.

By 2020, 30 percent of new construction in China will be green buildings, according to the Ministry of Housing and Urban-Rural Development. Retrofitting existing buildings for energy efficiency is also an important strategy. There are already more than 40 billion square meters of building space on the ground in China (about 5 times as much as in the United States). The Chinese government has launched a program to retrofit homes in colder areas, and in its current five-year plan, aims to retrofit 4 million square meters of nonresidential building space in ten cities, reducing each building’s average energy consumption 20 to 30 percent. That would be the equivalent of retrofitting 16 Empire State Buildings—one of the largest office buildings in the world.

The Chemsunny retrofit is an unusual case, given its recent construction and existing energy-saving features. But the building’s owner, the state-run chemical giant SinoChem, was keen to set an example. They invested about $2.85 million in the retrofit, an investment that is expected to cut about 1,700 tons of global warming pollution while saving roughly $250,000 each year in energy costs. Older buildings, which are the typical targets for retrofits, would probably see quicker payback times. A recent retrofit of an office building in Nanjing, built in 1997, has an expected payback period of about five-and-a-half years.

To generate energy savings, the Chemsunny retrofit focused on the innards of the building, rather than its envelope. The lighting and HVAC systems were upgraded, and computerized controls installed to monitor building systems and meter their energy use. Much of the work was entrusted to Johnson Controls, the Milwaukee-based engineering firm that also retrofitted the Empire State Building, in addition to its work on the Ministry of Science and Technology Building in Beijing, China’s first green building. The Chemsunny World Trade Center earned a LEED-Existing Buildings Platinum rating from the U.S. Green Building Council.

The carefully measured energy savings at Chemsunny will go into preparing a case study on payback time that can help influence other builders and property owners. The government is setting an example by investing in selected cities for retrofit demonstrations, and in fact, has a massive opportunity for energy savings simply by retrofitting some of the 16 billion square meters of space it owns in city civil buildings alone—more than double the entire commercial building space of the United States. But ultimately, retrofits need to take off in the private sector, and hard numbers on cost savings will help move the market.

A comprehensive package of government policies can help overcome market barriers to retrofits in the private sector. New York City’s Greener, Greater Buildings Plan targets the city’s largest buildings, and requires that owners publicly disclose building energy use, just as they would square footage and property tax. Owners are educated on energy-saving measures and can take advantage of special financing programs to get capital for energy efficient upgrades. Other facets of the program include rigorous standards for lighting efficiency, which end up being highly cost-effective for building owners, and a tenant engagement program to ensure that tenants and owners work collaboratively.

A report from NRDC and the Boston Consulting Group found that if all of China’s commercial and residential buildings, new and existing, could cut energy use by 70 percent and 55 percent, respectively, by 2015, China would cut 2 billion tons of global warming pollution. It’s an optimistic figure, but it does demonstrate the enormous upside of making buildings more energy efficient, not only for China, but for the planet.

I am the Executive Director of NRDC. The position is my second at NRDC. Beginning in 1994, I led the Clean Water Program for five years, before leaving in 1999 to serve as the head of the Environmental Protection Bureau for the Attorney General of the State of New York.

The trend in rich nations is to live less densely. Germans now live at less than 2 people per home on average and that number is still falling. If ten billion humans are to live at 2 people per house That means 5 billion homes.

A more realistic figure is 3 to 4 billion by mid century but that is still a big jump from the current circa 1B homes

These extra 3 billion homes even if efficient will need at least 30,000 TWh of primary energy.